Conventionally, percutaneous angioplasty is widely utilized in dilation treatment for narrowed area, an occluded area, and the like of a vascular lumen to restore or improve a blood flow in coronary artery, peripheral blood vessel, and the like. The balloon catheter for use in percutaneous angioplasty is generally structured such that an expansion balloon capable of inflation and contraction by adjusting an internal pressure is joined to a leading end of a shaft, and a lumen into which a guide wire is inserted (guide wire lumen) and a lumen that supplies a pressure fluid for adjustment of a balloon internal pressure (inflation lumen) are provided in the inside of the shaft along the longitudinal direction of the shaft.
A general example of PTCA (percutaneous transluminal coronary angioplasty) using such a balloon catheter is as described below.
First, the guide catheter is inserted from a puncture site in a femoral artery, a brachial artery, a radial artery, or the like, and a leading end of the guide catheter is positioned at the entrance of a coronary artery through a main artery. Then, the guide wire inserted into the guide wire lumen is advanced beyond the narrowed area in the coronary artery, and the balloon catheter is inserted along the guide wire and the position of the balloon is aligned with the narrowed area. Then, a device such as an indeflator is used to supply a pressure fluid to the balloon through the inflation lumen and inflate the balloon for dilation treatment of the narrowed area.
If there exists a plurality of narrowed areas in the lumens of the body, the expansion balloon may be inflated and then contracted at one site and then is passed through another site (re-cross) for expansion of the narrowed area.
The expansion balloon is structured by a columnar straight pipe part and tapered conical ends of the same. When the inflated balloon is contracted again, the straight pipe part and the taper parts of the balloon have wing parts and groove parts formed alternately, which constitutes a folding shape extended from the leading end to the base end of the balloon in the longitudinal direction. At that time, there may arise a flat phenomenon that a pair of opposed wing parts is extended in a radial direction, that is, a winging shape with the two wing parts. It is difficult to insert the thus shaped balloon into the narrowed area. Therefore, when being folded, the balloon is desirably shaped to have a large number of wing parts (three or more). Accordingly, the dimension of the balloon becomes shorter in the radial direction, which reduces a profile diameter of the balloon when being folded and facilitates passage of the balloon. To that end, various folding methods of balloon have been suggested.
For example, Patent Document 1 discloses a method for controlling folding of a balloon by which the cross section of the balloon is provided with film thickness distribution and the balloon folding is controlled by a difference in rigidity between a thin part and a thick part. However, when the balloon cross section is provided with film thickness distribution to ensure pressure capacity of the balloon, the film thickness of the thin part in the balloon tube is set according to the pressure capacity required for the balloon. Thus, it is inevitable that the thick part of the balloon tube becomes excessively thick, and as a result, the balloon becomes thick as a whole and the profile diameter of the balloon when being folded becomes larger. To make the entire balloon thin, it is necessary to reduce the film thickness of the thick part in the balloon, and in this case, it is not possible to ensure pressure capacity as stated above.
Meanwhile, besides initial passage of the balloon part through a narrowed area, it is important to, after expansion of the balloon, ensure passage (re-cross) of the balloon inserted into the same again or another narrowed area. It cannot be said that the balloon described in Patent Document 1 is high in insertion operability as a catheter because the initial passage of the balloon through a narrowed area is deteriorated. In addition, since there are large variations in film thickness of the balloon, there is a major problem that it is difficult to stably control folding of the balloon, which deteriorates re-cross capability. Further, it is necessary to provide the balloon tube with an excessive thickness difference before blow molding, which makes it very difficult to produce the balloon tube and the balloon using the balloon tube, thereby leading to reduction in molding yield.
In addition, Patent Document 2 discloses a method for controlling folding of a balloon by which a balloon tube having ribs formed by extrusion molding is used to provide the balloon with at least three ribs (grooves) on the inner surface thereof (in a thickness direction). However, as with the method described in Patent Document 1, the film thickness of a thinner rib part of the balloon tube is set according to pressure capacity required for the balloon, and thus the film thickness of the thicker side of the balloon becomes large excessively. As a result, the entire balloon becomes thick and the profile diameter of the balloon when being folded becomes large, which leads to a major problem that the balloon deteriorates in initial passage through a narrowed area and re-cross capability.
In addition, Patent Document 3 discloses a method for controlling folding of a balloon by which a mold is shaped in advance to have a plurality of longitudinal grooves continued at least in a long-axis direction and wing parts equal in number to the longitudinal grooves and corresponding to the longitudinal grooves, and a balloon is provided with the wing parts and the longitudinal grooves corresponding to a scroll-shaped cross section formed by concave grooves and convex streaks. As in the invention of Patent Document 3, forming the wing parts and the longitudinal grooves makes it possible to realize the balloon's stable folding tendency. However, if the balloon is shaped to realize a stable folding tendency, there is a problem that, when being expanded, the shape of the balloon does not become almost circular, and thus the thus shaped balloon cannot be used in clinical practice. In addition, the mold used for shaping the balloon has a very complicated shape, which results in waste of a large amount of time for product development and excessive increase of production costs. In these regards, there is still room for improvement in the invention of Patent Document 3.